1. Field of Invention
Exemplary aspects of the present invention relate to an apparatus for image forming, and more particularly, to a multifunctional image forming apparatus having at least two functions amongst the following, a printer, a digital copier, and a facsimile.
2. Description of the Related Art
Image forming apparatus such as printers, digital copiers, facsimiles and multifunctional peripherals (capable of serving at least two of the following functions, printer, copier and facsimile), generally include a sheet feeding device, a sheet conveyance device and an image output unit. The sheet feeding device feeds a transfer sheet to a sheet conveyance path. The sheet conveyance device conveys the transfer sheet along the sheet conveyance path. The image output unit outputs an image on the transfer sheet. The sheet conveyance path of the sheet conveyance device includes a plurality of conveyance rollers thereon. The conveyance rollers are rotationally driven by drive sources such as motors to convey the transfer sheet.
Such image forming apparatuses can register the sheet position and image position in a direction (hereafter referred to as a side direction) perpendicular to a sheet conveyance direction. The sheet position in the side direction needs to be corrected at an upstream side from a position in which the image is output on the transfer sheet so that the image can be formed on an accurate position of the transfer sheet in the side direction. This correction of position is hereinafter referred to as a side registration adjustment, which will be described with reference to FIG. 1.
FIG. 1 illustrates an example of the related art side registration adjustment mechanism in a related art image forming apparatus.
The related art image forming apparatus includes a contact image sensor 210, a control unit 230, a shift unit 250, a pinion gear 280, a shift motor 290, and an eccentricity cam 300. The shift unit 250 includes a driving motor 320, a side plate 330, rotation axis 340, registration rollers 180, a spring 310, and a registration roller gear 270. As shown in FIG. 1, the rotation axis 340 is supported by a side plate (not shown) and the side plate 330 at respective ends thereof. The registration roller axis 340 includes the plurality of registration rollers 180 thereon and the registration roller gear 270 at a side of the side plate 330. The driving motor 320 is disposed on the side plate 330 to rotationally drive the pinion gear 280. The pinion gear 280 engages with the registration roller gear 270, and thereby, the registration rollers 180 are rotated through the rotation axis 340.
The side plate 330 is movably installed in the related art image forming apparatus so as to move in the side direction by a bias applied by the spring 310. For example, the spring 310 applies a bias towards an apparatus frame 260 (i.e., a direction XX2). The side plate 330 is held at a position where the side plate 330 contacts the eccentricity cam 300 that is rotated by the shift motor 290. Therefore, the side plate 330 moves in the directions XX1 and XX2 when the eccentricity cam 300 is rotated. The registration rollers 180 and the driving motor 320 also move in the directions XX1 and XX2 when the eccentricity cam 300 is rotated. The control unit 230 controls the driving of the driving motor 320 and the shift motor 290.
The registration rollers 180 register a transfer sheet 200 conveyed in a direction YY, indicated by an arrow in FIG. 1. For example, the pair of registration rollers 180 (a lower registration is not shown) sandwich the transfer sheet 200, and the contact image sensor 210 detects a position of one side of the transfer sheet 200 in the side direction. The transfer sheet 200 illustrated by a solid line in FIG. 1 achieves a shifted state in which one side of the transfer sheet 200 is shifted from a reference position SS illustrated by a dotted line. The reference position SS in the side direction represents a suitable position with respect to the image to be output thereon. When one side of the transfer sheet 200 is shifted from the reference position SS in the side direction as shown in FIG. 1, the shift unit 250 moves the transfer sheet 200 towards the direction XX1 with a movement thereof. After the transfer sheet 200 passes through the registration rollers 180, the shift unit 250 moves towards the direction XX2 so as to return to an initial position. The contact image sensor 210 detects an edge position of the transfer sheet 200 in the side direction so that the control unit 230 determines a movement distance Δ′X of the transfer sheet 200 in the direction XX1. Since the image is output assuming that the side edge of the transfer sheet 200 is located at the reference position SS, the side registration adjustment can be appropriately performed when the transfer sheet 200 is conveyed along the reference position SS in the side direction.
One example attempts to control the movement distance of a transfer sheet by using a memory mechanism. The movement distance of the transfer sheet determined by a shift unit and information on the transfer sheet such as thickness, quality and type are correlated and stored in the memory mechanism beforehand. Thereby, the movement distance of the transfer sheet is controlled based on the information stored in the memory mechanism.
However, when the transfer sheet is shifted in the side direction in a relatively large amount, the movement distance of the transfer sheet increases. In a successive printing operation, the shift unit moving to move the transfer sheet in the side direction has to return to an initial position before a next transfer sheet is conveyed thereto. In other words, when the movement distance is relatively large, the movement speed of the shift unit needs to be increased by using a high power motor. However, such a high power motor is costly.
In attempting to solve such a cost problem, a technique in that the side position of a transfer sheet is adjusted by adjusting the position of a sheet feeding unit is proposed. However, it is difficult to adjust the sheet feeding unit such as a sheet feeding cassette and a sheet hopper such that a side position of the transfer sheet matches with the reference position in the side direction.